This invention relates to a process for the preparation of supported catalysts, including fluid-bed catalysts by the impregnation of a pre-formed support with at least one metal alkoxide. The present invention also is directed to a process for the preparation of fluid-bed catalysts containing the mixed oxides of vanadium and phosphorus by the impregnation of a pre-formed fluidizable support with a vanadium alkoxide and subsequent reaction with a phosphorus containing compound. The vanadium phosphorus oxide containing fluid-bed catalyst is useful for the production of maleic anhydride from hydrocarbons, such as n-butane, n-butenes, 1,3-butadiene or mixtures thereof.
Fluid-bed catalysts have conventionally been prepared in various ways. In one method of preparation, catalyst component containing compounds and support materials are contacted in a solution or slurry, possibly with heating, and the mixture is thereafter dried. The resulting solid is then ground and screened to a proper fluidizable size, such that the catalyst particles have a particle size of about 20 microns to about 300 microns.
Another method of preparation of fluid-bed catalysts is the oil drop technique, in which a solution or slurry of catalyst components and support materials are dropped into a hot oil bath, to form substantially microspheroidal particles capable of fluidization. Another method of preparation includes the spray drying of a solution or slurry of catalyst components and support material to obtain microspheroidal particles.
Another method for obtaining supported catalysts is by the impregnation of a previously formed and commercially available fluidizable support material with a solution of the catalyst or the catalyst components.
When the catalyst components and support materials are mixed toeghter, it is necessary in order to obtain suitable physical integrity for the fluidizable catalyst, to precisely match physical characteristics and affinities of the catalytic and support components so that these might bind more readily, whether physically or chemically, to withstand the attritting forces of commercial fluid-bed reactors. To attain proper attrition resistance, it is often required that particular proportions of support material versus catalytic material be achieved in the mixture. If the catalyst components are mixed before the fluidizable catalyst particles are formed, then a certain portion of the fluidizable catalyst particles so formed may lack the required proportion of support material. If a lesser amount of support material is incorporated, the attrition resistance will be lessened and the particle will be subject to attrition or fracture during use. If too great a portion of support material is present in the catalyst particle, the catalytic activity of that particle may be diminished.
One method for obtaining attrition resistant particles is to use an attrition resistant fluidizable support material which has been pre-formed. When these supports are impregnated with the catalytic material, however, maximum catalytic efficiency is not readily achieved.